fix: brainstorm infinite loop, ghost cursor, embedding ::vector cast, semantic search, billing stats, usage meter accordion

- Fix useBrainstormSocket: stable guestId via useRef, remove setState in cleanup
- Fix GhostCursor: direct DOM manipulation via refs, no useState re-renders
- Fix all SQL embedding queries: add ::vector cast on text columns
- Fix embedding truncation to 15000 chars (under 8192 token limit)
- Fix NoteEmbedding INSERT: remove non-existent updatedAt column
- Fix billing page: show all quota stats in grid instead of single metric
- Fix usage meter: accordion expand/collapse, per-feature detail
- Fix semantic search: rebuild 103 note embeddings, ::vector cast on vectorSearch
- Fix brainstorm expand/manual-idea/create: ::vector cast on embedding SQL

memento-note/components/admin-sidebar.tsx

@@ -122,7 +122,7 @@ export function AdminSidebar({ className }: { className?: string }) {
           </DropdownMenu>
 
           <a
-            href="/"
+            href="/home"
             className={cn(
               'flex min-w-0 flex-1 items-center gap-2 rounded-xl px-2 py-1.5 transition-colors',
               'hover:bg-white/40 dark:hover:bg-white/10'
@@ -143,7 +143,7 @@ export function AdminSidebar({ className }: { className?: string }) {
         </div>
 
         <a
-          href="/"
+          href="/home"
           className={cn(
             'flex items-center gap-3 rounded-xl px-4 py-2.5 text-[13px] font-medium transition-all',
             'text-muted-foreground hover:bg-white/40 hover:text-foreground dark:hover:bg-white/10'